The YAG laser has an excellent characteristic that makes beam transmission with optical fibers. In addition, the oscillator of the several kW class has been developed, and so its applications are changing largely from conventional one. The authors have adopted the high power YAG laser welding and surface treatments that uses optical fibers favorable to application to narrow, complicated areas.
In this paper, the authors showed the fundamental beam intensity distribution analysis in focusing lens, optical fiber and kaleidoscope beam homogenizer for high power YAG laser. Then, we have designed and manufactured the compact lens system, metal mirror which have high reflectivity and durability and kaleidoscope. And we also showed the beam transmission characteristics in optical fibers. In addition, on the basis of those elementary techniques, some practical applications with high power YAG laser have described.

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Much attention is recently paid to laser surface modification (LSM) techniques forproviding an approach in controlling compositions and structure of matal surface. IHI has been performing reseach activity for bringing LSM techniques to a degree of development such that they can be used industrially. One of these LSM techniques was actually applied to austenitic stainless steel pipes put in practical use to prevent stress corrosion cracking.
In this paper, our recent laser beam technology related to LSM and details of LSM technique applied to actual component in our company are introduced.

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In this review, a nobel technique in laser high-speed drilling for Teflon films reinforced with SiO₂ particles has been introduced. The new laser drilling surpasses conventional techniques in simplicity, throughput and spatial resolution. The process consists of three simple steps. First, a thin absorbing layer (300 A gold) is deposited on a Teflon film to allow laser absorption. Second, the drilling is performed by pulsed laser irradiation at a rate of one hole per pulse. The irradiation does not completely open the holes in which debris still remains. Third, ultrasonic cleaning in water is used to remove the modified and weakly bound materials inside the drilled holes, leaving behind 50 μm diameter through holes in 25 μm thick teflon sheets. This new laser process is useful for packaging technology because of its drilling speed as high as 60, 000 holes per minute, and its inexpensive equipment cost.

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An argon-fluoride (ArF) excimer laser-induced chemical vapor deposition (LCVD) technique has been developed for fabrication of soft X-ray multilayer mirrors. Film thickness distribution is controlled by scanning a laser beam on the substrate. Tungsten-carbon (W/C) and tungsten-silicon (W/Si) multilayers with a uniform film thickness are deposited and characterized from soft X-ray reflectivity measurement. Furthermore, a W/Si multilayer with laterally varying film thicknesses is successfully fabricated, and the feasibility of LCVD was demonstrated for fabricating multilayer mirrors for high performance soft X-ray focusing systems.

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Lasers are regarded as an effective tool for machining ceramics; however, there exists a difficulty in improving the removal rate, because of physical properties of ceramics, such as low fracture toughness, high decomposition temperature, and melting point. To solve this problem, we attempted laser machining of half-sintered ceramics. Since half-sintered ceramics have many pores which would arrest crack propagation and low thermal conductivity, relatively slight damage and high removal rate can be expected. In this study, a laser beam of a Qswitched YAG laser was scanned on the surface of specimens to form shallow grooves. Effects of porosity of the workpieces, pulse frepuency and peak power on the removal rate were examined experimentally.
The removal rate of the half-sintered specimens was found to be about 20 times as large as that of perfect-sintered ones. With an increase in the peak power of pulses, the removal rate increased greatly. The half-sintered specimens turned black near the irradiated area with no ascents of the density and hardness observed

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The paper describes characteristics and formation mechanism of laser PVD films, which were deposited on Ti or other metallic substrates from Si₃N₄ or SiC ceramic targets in wide ranges of chamber pressure and substrate temperature by using CW Nd: YAG laser as an evaporator. Many small crystalline Si₃N₄ particles of 1 to 15 μm size in globular orgranular shapes and metallic Si particles in the hemispherical shape were observed in the flat and dense amorphous LPVD films from the Si₃N₄ target. Such particles are due to spatters ejected as the fraction of solid and/or Si liquid from the target surface. Nitrogen contents in the amorphous films were reduced considerably because Si₃N₄ was decomposed into Si and N on the laser irradiated site. Hard films of 8-12 GPa in Knoop hardness were obtained at the substrate temperature of 723-923 K under the pressure of 0.02-1 Pa. In the case of SiC, small granular particles of less than 5 pm were observed in the flat and smooth film. The SiC films ranging 10-36 GPa under the conditions of 623-873 K in substrate temperature and 0.03 Pa in pressure were much harder than those of Si₃N₄. The results of scratch test indicated that the adhesive strength of the LPVD film was better in the case of Ti than in the case of W. TEM observation of films or clusters formed on the Carbon substrate revealed that the evaporated atoms deposited directly on the substrate forming a dense amorphous film under the high vacuum of 0.01 Pa. On the other hand, under the pressure of more than 1 Pa, clusters or ultra-fine particles were once formed on the substrate and were transformed into the film by the thermal migration on the heated substrate.

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This paper describes methods of coloring glass layers formed on the surface of a cement composite by laser irradiation. We found that blue and green coloured glass layers are obtained easily by the addition of Co-base and Cr-base pigments to mortar whereas yellow and pink are difficult to obtain.This is because glass formation temperatures are higher than yellow and pink color formation temperatures and, in addition, the constituents of cement and aggregate tend to obstruct coloring. To obtain luster colours, we found necessary to add a transparent glaze to the mortar composition. The addition of glaze lowers glass formation temperatures and reduces the relative Volume of cement and aggregate. The relative ease of obtaining blue and green colors compared to yellow and pink is explained by considering the mechanisms of color formation.

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40mm by 40mm large size YBa₂Cu₃O_7-x high temperature superconducting thin films were fabricated by a pulsed laser deposition. A high energy ArF excimer laser up to 1.2J/pulse and a substrate-rotation deposition technique with substrate off setting to the center of the plume were developed for making large area thin films.The ArF excimer laser has a newly developed back UV-preionization system and a high precision high voltage trigger cirouit and utilizes a LC inversion voltage doubling circuit for high voltage discharge. To improve an energy profile of ArF laser beam, a segment mirror was also developed. Large area superconducting thin films were deposited with the shaped high energy ArF excimer laser of 0.58J on the surface of the target and the substrate rotation technique with off setting distance of40mm. The superconducting thin film has thickness variation less than10% and superconducting transition temperatures between 85K to 90K over the whole substrate.

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A design of a beam homogenizer which consists of kaleidoscope and lens optics is described. The beam intensity uniformity of ±8% and the pattern edge sharpness of 0.1mm were obtained with the excimer laser beam homogenizer constructed with the low spherical aberration (<10μm) imaging lens and the kaleidoscope carefully designed with a beam uniformity simulation code.

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In order to improve the capabilities of the exicimer laser ablation apparatus thatuses an imaging optical system, we have been developing an innovative multiple irradiation optical system, which utilizes laser energy more efficiently than a conventional optical system. In our system, a reflector is placed opposite the mask, and the mask surface is made of a highly reflective coating. In this optical system, a laser beam irradiates the mask repeatedly, and the laser energy is used more efficently than in the conventional optical system. Experimental results show that, in comparison with the conventional optical system, our system is 12 times energy efficient.

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